I think a lot depends on where you live, and your own circumstances.
I've lost four cats over 20 years to the roads, two of which have been in the last three years, and it's heartbreaking.
Our neighbour's cat was also knocked down and killed just two weeks ago. As he used to play with our two, it upset me greatly.
Me and OH can't agree over this indoor/outdoor business. I would prefer to cat proof our garden, so the cats have access to the outdoors but in a limited way. OH doesnt feel this is natural and would be unkind to the cats. However, I know many people who have cat proofed gardens which work well as a solution, and other with indoors only cats, and they're perfectly happy so long as they get plenty of stimulus and playtime, and a decent window to look out of.
I agree though that most of the time, once they do get outdoors and their confidence grows, you'd have the devil's own job keeping them in again.